Control apparatus for hydraulic equipment

ABSTRACT

A control valve assembly for controlling hydraulic pressure comprising a non-adjustable unloader valve for large escape flow connected in parallel with a small adjustable trigger valve. The trigger valve opens when the pressure rises to an adjustable predetermined valve and exposes to this pressure on actuating piston of the unloader valve which is thereby opened. Means are disclosed for adjusting the closing characteristics of the unloader valve.

United States Patent Norton et al. [4 1 Sept. 19, 1972 [5 CONTROL APPARATUS FOR 2,225,916 2/1940 Maglott 1 37/4895 HYDRAULIC EQUIPMENT 2,293,l l8 8/1942 Cumming 1 37/4895 l t s v I n l Buckingham Nomm Douglas m 3,203,320 8/l965 Alfieri ..137/4s9.s x

a" of Norton s n Frantz gland Primary Examiner--M. Cary Nelson Assignee: Norton Tool p y Limited, Assistant Examiner-David R. Matthews Surrey, England Att0rney-Watson, Cole, Grindle & Watson [22] Filed: Jan. 5, 1971 [57 ABSTRACT 21 Appl. No.: 104,097

A control valve assembly for controlling hydraulic pressure comprising a non-adjustable unloader valve [52] US. Cl. ..137/489.5 for large escape flow connected in parallel with a .-F16k small adjustable gg valve. e r gge v e opens [58] Field of Search ..l37/l 10, 115, 118554189252, when the pressure rises to an adjustable predetep mined valve and exposes to this pressure on actuating piston of the unloader valve which is thereby opened. [56] References cued Means are disclosed for adjusting the closing charac- UNITED STATES PATENTS teristics of the unloader valve.

1,668,128 5/1928 Ruths ..25 1/122 X 4 Claims, 3 Drawing Figures L I llllllllllllllll I CONTROL APPARATUS FOR HYDRAULIC EQUIPMENT This invention relates to control apparatus for hydraulic equipment and is particularly concerned with a valve assembly for venting fluid from a hydraulic system on the attainment of a predetermined high pressure in the system, the venting passage remaining open until the pressure has dropped to a much lower predetermined value.

The invention is applicable generally to hydraulic apparatus in which such a venting or unloading of hydraulic pressure from a high level to a low level is required. A particular application is for the control of a double acting hydraulic ram apparatus of the kind which is the subject of U.S. Pat. No. 3,033,170 to Henry Norton et al.

That apparatus may have control apparatus of the general type described in U.S. Pat. No. 2,980,064 to Henry Norton et al. The present invention constitutes an improved form of control apparatus suitable for that purpose. In the control apparatus described in U.S. Pat. No. 2,980,064 Henry Norton et al. there is an unloader valve communicating with the pressure chamber of the ram and arranged to open and vent the pressure chamber when a predetermined high pressure is attained, the unloader valve comprising a cylinder containing a spring-loaded piston of relatively large area controlling a port in the cylinder wall and acting on a closure member which can seat on a seating of much smaller area than the piston and which communicates with the pressure chamber of the ram, such that the closure member is lifted from its seating on the attainmentof the predetermined high pressure and a space on the closure member side of the piston thereupon communicates with the pressurechamber. The value of the predetermined high pressure at which the springloaded piston is moved to allow the closure member to lift from its seating is adjustable by adjusting the loading of the spring which acts on the piston. The closure member, when opened, must expose a passage large enough for the net outflow from the ram on the return stroke plus the flow from the pump which continues to deliver during the return stroke. In the case of a large system and/or a rapid ram return rate the unloader valve must be of substantial size to permit the necessary high rates of fluid flow therethrough. This means that the spring acting on the piston must be very strong so that the force required to adjust it is considerable. It is an object of the present invention to provide an improvement which enables the value of the predetermined high pressure at which the unloader valve will open to be adjusted without having to vary the loading of a strong spring.

According to the present invention a control valve assembly for hydraulic equipment comprises an unloader valve having a cylinder containing a springloaded piston controlling a port in the cylinder wall and acting on a first valve in permanent communication with a part of the hydraulic system in which the pressure is to be controlled, this valve being partially pressure-balanced with regard to the said pressure, and a second valve also in permanent communication with the said part of the hydraulic system and which can seat on a seating of smaller cross-sectional area than the seating of the first valve and loaded by an adjustable spring, the downstream sides of the first and second valves being in permanent communication with the cylinder space on the sideof the piston opposing its spring loading.

The spring of the second valve can be light owing to the small area of this valves seating, and is adjusted so that the second valve opens when "the pressure attains the predetermined high value, whereupon pressure fluid is admittedto the cylinder space, moving the piston against its spring. This permits the larger first valve to open and alsocauses the piston to expose the port in its cylinder wall. The opening of the larger first valve permits the venting of a substantial volume of fluid from the system; a much larger volume than is possible through the second valve. The second valve therefore acts as a trigger or relay valve to cause the larger first valve to open. The first valve should be large to permit a large flow of fluid whereas the second valve should be small so that it can have alight spring.

The adjustment of the value of the pressure at which the second valve opens and triggers the unloading is effected by adjusting the loading of the light spring which acts upon it. Since the adjustment is effected at this point and not at the piston itself, the heavy spring which acts on the piston can be non-adjustable.

An adverse effect of having an adjustable spring acting on the piston as in the known type of valve apparatus described in U.S. Pat. No.2,980,064 to Henry Norton et al. is that the value of the low pressure at which the piston will close the ports will vary, depending upon theadjustment of this spring. As described in U.S. Pat. No. 2,980,064 to Henry Norton et al. the operating characteristics of the ram can be controlled by controlling the rate of outflow from the cylinder space after the ports have closed, e.g., by providing an.

adjustable auxiliary escape orifice. For a given orifice size the rage of outflow. will depend upon the pressure. Thus, if the spring acting on the piston is adjustable, the setting of the orifice size necessary to produce a given effect will not be constant but will vary depending upon the adjustment of the spring. The improvement which is the subject of the present invention enables a constant value for the said predetermined low pressure to be maintained independently of adjustments of the said predetermined high pressure so that a given setting of the orifice size will produce the same effect irrespective of the adjusted value of the predetermined high pressure.

Instead of providing an adjustable orifice, e.g., an orifice finely adjustable by means of a taper needle which can be screwed in or out, to control the operating characteristics, there can be a movable adjusting member which is adjustable in steps, e.g., which is arranged to expose any of a plurali'ty of orifices of different sizes, whereby a selected orifice of appropriate size can be brought into operation when it is desired to alter the operating characteristics, e.g., in the case of a hydraulic press, between single stroking, long stroke automatic stroking and short stroke vibratory stroking.

As already mentioned the first valve is of the partially pressure-balanced type. This enables a lighter spring acting on the piston to be used, as this spring does not have to act against the full pressure of the hydraulic system. The valve must not be fully pressurebalanced as if it were there would be no force tending to cause it to open. The first valve may be such that the end of it which is remote from the seating is exposed to atmosphere or to a region at about atmospheric pressure. In this case the valve will be held against its seating not only by the pressure of the spring but also be any residual pressure in the cylinder space. In another form of the invention the end of the first valve remote from the seating is enclosed in a chamber which is maintained at the same pressure as the cylinder space, e.g., by means of porting in the variable housing or through the valve itself. In this case the valve is maintained on its seating only by the force of the spring acting on the piston substantially unaided by hydraulic forces.

The invention may be performed in various ways, and some embodiments will now be described by way of example with reference to the accompanying diagrammatic drawings, in which:

FIG. 1 is a section through one form of control valve assembly embodying the invention;

FIG. 2 is a fragmentary section through a modified form of the first valve; and

FIG. 3 is a fragmentary section through a further modified form of the first valve.

In the various figures, identical or equivalent parts have been given the same reference numerals throughout.

Referring to FIG. 1 of the drawings, the control valve assembly comprises an unloader valve enclosed within the broken line frame 11 and a trigger or relay valve 12 enclosed within the broken line frame 13. The control valve assembly is for the purpose of venting, through an outlet port 14, hydraulic fluid from a hydraulic system 15 via a line 16, on the occurrence of a'predetermined high pressure in the line 16, the path from the system 15 to the outlet 14 then remaining open until the pressure in the line 16 has dropped to a much lower predetermined value.

The line 16 has two branches 17 and 18. The branch 17 goes to the unloader valve 10 and the branch 18 goes 'to the trigger or relay valve 12. Flow through the unloader valve 10 is normally blocked by a valve 19 (the first valve) which seats on a seating 20, being held against the seating by the action of a strong, nonadjustable spring 21. Flow through the trigger or relay valve 12 is normally blocked by a valve 22 (the second valve) which is held against a seating 23 by the action of a spring 24. The loading of the spring 24 can be adjusted by means of an adjustable screw abutment 25. The area of the seating 23 of the second valve 22 is small so that the spring 24 can be relatively weak. Consequently the force necessary to adjust its loading is small. On the other hand, the area of the seating of the first valve 19 is large, to permit a large flow from the system 15 when the unloader valve 10 is open. The chamber 26 to the right of the second valve 22 in FIG. 1 communicates with a chamber 27 to the right of the first valve 19 by means of a conduit or passage 28. Thus, when the pressure in the line 16 rises to the predetermined high value at which the trigger or relay valve 12 is set to open (this value being predetermined by the setting of the ajustable abutment the second valve 22 is moved from its seating 23 and the pressure of the fluid in the line 16 is transmitted via the chamber 26 and the conduit 28 to the chamber 27 of the unloader valve 10. The pressure there acts on a piston 30 which forms the right-hand wall of the chamber 27.

The area of the piston 30 is large compared to that of the first valve 19, and moreover this valve is partly pressure-balanced with regard to the pressure in the branch 17 as described below. The strength of the spring 21 is such that although it can easily hold the first valve 19 closed against the pressure in the line 16 transmitted via the branch 17, it is not nearly strong enough to withstand this pressure when acting on the larger area of the piston 30, as transmitted via the branch 18, the second valve 22 and the conduit 28. The piston 30 is therefore moved to the right to expose the port 14 and allow fluid to escape rapidly from the system 15 via the line 16, the branch 17 and the now open first valve 19. There will also be a small escape flow through the parallel path consisting of the branch 18, the open second valve 22 and the conduit 28.

Since the pressure of the fluid upstream of the port 14 continues to act on the area of the piston 30, this piston will continue to expose the port 14 until the pressure has fallen substantially. When this has occurred and the port 14 has been obstructed, the first valve 19 will still not be fully closed. To permit complete-closure a second fluid outlet 31 is provided, which includes an orifice 32 adjustable by a control screw 33. The pressure upstream of the orifice 32 depends onthe force of the spring 21, and since this spring is non-adjustable, a given setting of the control screw 33 will produce the same effect irrespective of the setting of the adjustable abutment 25, i.e., independently of the pressure at which the control valve assembly is set to open.

As mentioned above and illustrated in FIG. 1, the first valve 19 is partly pressure-balanced as regards the pressure in the branch 17, having connected to it by a stem 35 a land 36 which is a sliding fit in a cylindrical bore 37 on the opposite side of the branch 17. The effective area of the first valve 19 is nevertheless greater than that of the land 36, so that the pressure in the branch 17 exerts a small net opening force on the valve member 19. On the other hand, the pressure in the chamber 27 which tends to hold the first valve 19 on its seating acts over the whole effective area of this valve. In this way the spring 21 can be lighter than would otherwise be necessary.

In the modified embodiment shown in FIG. 2, the first valve 19 is partly pressure-balanced also as regards the pressure in the chamber 27, so that its movements are essentially determined only by the spring 21, the net hydraulic forces acting upon it being minimal. For this purpose the end 41 of the bore 37 is closed to define a chamber 42 which is in permanent communication with the valve chamber 27 through a passage 43 in the valve 19. This communication could equally well be established by a passage 44 in the body of the first valve 10 instead of by a passage in the valve 19. Further, this valve could be fully pressure-balanced against the pressure in the chamber 27, by providing a head on the left-hand end of the valve of the same diameter as the seating 20.

FIG. 3 shows a further modification, in this case relating to the control of the escape of fluid from the valve chamber 27 after the piston 30 has closed the outlet port 14. In place of a control screw 33 with a tapered end which controls a single orifice 32 as shown in FIGS. 1 and 2, there is provided a control screw 46 having a flat end 47 which, as the screw is moved in or out, successively closes or opens a plurality of orifice ports 48, 49, 50. Thus, in this embodiment, the escape of fluid is adjustable step-by-step. This is of advantage if, say, there are only three different operating conditions required which are controllable by the screw 46 because the risk of incorrect setting of the control screw 46 is minimized.

What we claim as our invention and desire to secure by Letters Patent is:

l. A control valve assembly for hydraulic equipment having a part in which the hydraulic pressure is to be controlled, said assembly comprising:

i. an unloader valve unit having a cylinder, a piston slidable in said cylinder, means defining a port in said cylinder closable and exposable by said slidable piston, first spring means in said cylinder acting on said piston, a'first valve, a first seating for said first valve, said piston contacting said first valve, and said first spring means urging said piston in a direction to hold said first valve on said first seating, conduit means placing said first seating in permanent communication with said part of said hydraulic system, said cylinder and said piston defining a first chamber on the side of said first valve opposite to said conduit means, said first chamber being in communication with said port when said port is exposed by said piston, further piston means in permanent communication with said part, said further piston means being of smaller area than said first seating, and means connecting said further piston means to said first valve to partially pressure balance said first valve with regard to the pressure in said part;

ii. a trigger valve unit comprising a second valve, a second seating for said second valve smaller than said first seating, second spring means urging said second valve toward said second seating, means to adjust the loading of said second spring means, conduit means placing said second seating in permanent communication with said part of said hydraulic system, means defining a second chamber on the side of said second valve opposite to said last-mentioned conduit means; and

iii. conduit means placing said first chamber in permanent communication with said second chamber.

2. A control valve assembly according to claim 1, in which said first spring means is non-adjustable and which includes:

iv. adjustable fluid flow control? means to control fluid outflow from said cylinder of said unloader valve unit independent of said port.

3. A control valve assembly according to claim 2, in which said adjustable fluid flow control means is adapted selectively to open and close a plurality of fluid flow ports.

4. A control valve assembly according to claim 1, including means to at least partly pressure-balance said first valve as regards the pressure in said cylinder. 

1. A control valve assembly for hydraulic equipment having a part in which the hydraulic pressure is to be controlled, said assembly comprising: i. an unloader valve unit having a cylinder, a piston slidable in said cylinder, means defining a port in said cylinder closable and exposable by said slidable piston, first spring means in said cylinder acting on said piston, a first valve, a first seating for said first valve, said piston contacting said first valve, and said first spring means urging said piston in a direction to hold said first valve on said first seating, conduit means placing said first seating in permanent communication with said part Of said hydraulic system, said cylinder and said piston defining a first chamber on the side of said first valve opposite to said conduit means, said first chamber being in communication with said port when said port is exposed by said piston, further piston means in permanent communication with said part, said further piston means being of smaller area than said first seating, and means connecting said further piston means to said first valve to partially pressure balance said first valve with regard to the pressure in said part; ii. a trigger valve unit comprising a second valve, a second seating for said second valve smaller than said first seating, second spring means urging said second valve toward said second seating, means to adjust the loading of said second spring means, conduit means placing said second seating in permanent communication with said part of said hydraulic system, means defining a second chamber on the side of said second valve opposite to said last-mentioned conduit means; and iii. conduit means placing said first chamber in permanent communication with said second chamber.
 2. A control valve assembly according to claim 1, in which said first spring means is non-adjustable and which includes: iv. adjustable fluid flow control means to control fluid outflow from said cylinder of said unloader valve unit independent of said port.
 3. A control valve assembly according to claim 2, in which said adjustable fluid flow control means is adapted selectively to open and close a plurality of fluid flow ports.
 4. A control valve assembly according to claim 1, including means to at least partly pressure-balance said first valve as regards the pressure in said cylinder. 